Why are we seeing more white sharks and seals in the Gulf of Maine?

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While they may seem like newcomers, white sharks (Carcharodon carcharias) are native to the Gulf of Maine and have historically inhabited the waters along the coasts of the Northeast U.S. and Canadian Maritimes as well as offshore in the Northwest Atlantic Ocean. 

Though the Gulf of Maine makes headlines for rapidly warming waters and other adverse impacts of climate change, warmer waters are not necessarily the reason for more white sharks. The increased sightings and presence of white sharks in New England waters are largely due to marine conservation and fisheries management efforts over the last several decades – representing a conservation and management success story. Increasing shark populations may be a sign that the marine food web is rebounding after generations of exploitation. Robust populations of apex predators like sharks are considered to be signs of a healthy ecosystem and indicators of recovering prey populations and improved biodiversity.

Seals, like sharks, play an important role in our healthy marine ecosystems. Seals are also native to the Gulf of Maine but were nearly eradicated in Northwest Atlantic waters due to hunting and culling before legal protections were established in the 1970’s. Long-standing conflicts between humans and seals were related to perceived impacts of marine mammals on economically valuable fishery resources, based on beliefs that seals consume “too many” fish and introduce parasites that infect and reduce the value of landed fish stocks. Interactions between seals, fish, and people remain a complicated topic for marine policy and management.

Both white sharks and seals in the Gulf of Maine experienced dramatic population declines at the hands of humans and their populations have only recently begun to recover. In the 1970’s, key legislation related to marine mammals and fisheries changed the policy and management landscape in U.S. waters by restricting and managing harvests and providing legal protection for certain species. 

Today, the exact population numbers for white sharks in the Northwest Atlantic Ocean (including the Gulf of Maine) are unknown due to wide ranges of seasonal migration and foraging patterns – which is the case for many marine species. 

For seals, population estimates are determined by stock assessment reports, which are required under the U.S. Marine Mammal Protection Act (MMPA). The harbor seal population is estimated at 70,000 individuals (potentially declining). For gray seals, the population estimate is approximately 27,000 in U.S. waters based on pup production, and over 500,000 in the Northeast Atlantic including Canadian waters. (Source: https://www.sealconsortium.org/faq).

Sightings of white sharks in the Gulf of Maine are relatively rare, and reports tend to come from vessels at sea or a predation event on a marine mammal. Sightings data, catch records, and tagging data indicate that white sharks usually occur in the Gulf of Maine region from the early summer through the fall. On Cape Cod, for example, white shark activity typically peaks in August.

It is important to remember that seals are not the only food source of white sharks. Although some large white sharks eat seals, their diet includes other marine life like fish and other marine mammal carcasses. It is not fully understood how seal populations influence the abundance, distribution, or behavior of white sharks. However, experts believe that shark attacks on people are often caused when white sharks mistake a human for a seal.

As conservation and management efforts in the Gulf of Maine ecosystem restore populations of marine life, we expect to see examples of species interactions that appear to be “new” to us given our frames of reference and ways of living. However, before human impact on our ecosystems, these species and interactions would have been more common – for example, white sharks hunting seals in New England waters. Additionally, we know that human populations and development along our coasts have greatly increased, and with that, human interactions with marine animals like sharks and seals will become more frequent. Put simply, more people in the water and more sharks can lead to more human-shark interactions.

"It is important to remember that shark attacks remain very, very rare. White shark populations in the region have been increasing for at least the past two decades, largely without notice."

- DR. NATHAN FUREY, ASSISTANT PROFESSOR OF BIOLOGICAL SCIENCES AT THE UNIVERSITY OF NEW HAMPSHIRE

Even though interactions between sharks and humans remain rare, those using our marine waters can be proactive. This includes exercising caution when seals are in the area or if large schools of fish are present. If you are in the water and notice animals exhibiting strange behavior such as attempting to hide using surfboard or flotation device, be vigilant and get out of the water. In addition, avoid being alone in the water or during dawn or dusk. 

It is important to develop informed opinions and make fact-based decisions about our coastal/marine resources and our experiences in, on, or near the water. We hope that this information will help New Hampshire’s coastal residents, visitors, beachgoers, swimmers, surfers, fishermen, boaters, and others better understand why and how human-shark interactions occur and how to stay safe.

NH Sea Grant has compiled a page of information and resources about shark safety and facts for New Hampshire: 

VISIT OUR SHARK RESOURCES AND FACTS PAGE

This story has been reviewed by Dr. Nathan Furey, assistant professor of biological sciences at the University of New Hampshire, Dr. Andrea Bogomolni, chair of the Northwest Atlantic Seal Research Consortium, and Dr. Erik Chapman, director of NH Sea Grant.

Questions? Contact: nh.seagrant@unh.edu

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